This invention relates generally to the production of GaAs semiconductor devices and more particularly to a method for constructing systems of refractory layers for GaAs semiconductor devices having a gold electrode.
Refractory layer systems in GaAs semiconductors provide both a Schottky barrier with the GaAs and a diffusion barrier between the GaAs and the gold conductor. Existing methods for manufacturing GaAs semiconductors utilize systems of refractory layers which include metals or combinations of metals that are different from those of the present invention. The layers formed by current methods are deposited on a GaAs wafer at approximately room temperature and typically within a vacuum. The wafer is then removed from the vacuum and annealed at temperatures as high as 800.degree. C. Devices fabricated with existing refractory systems fail from exposure and continuous use of more than a few hours at high stress temperatures above 450.degree. C. because of interdiffusion between the gold layer and the GaAs, and variations of the Schottky barrier due to both interdiffusion and the formation of interfacial layers between the barrier layer and the GaAs. Removal of the wafer from the vacuum before annealing may expose the wafer to contaminants and thereby reduce its reliability. The high processing temperatures tend to degrade the characteristics of the GaAs when forming semiconductors using vertical technology. The Schottky barriers thus formed, however, are thermally stable at high temperatures, but only for a short time ranging from a few minutes to a few hours. High-temperature heat treatment is also unsuitable for semiconductors formed by planar technology because of degradation to the GaAs and both the isolation layer, typically silicon dioxide (SiO.sub.2), and the metal-semiconductor interfaces existing in a planar structure. Consequently, existing semiconductors formed by planar technology are developed using lower processing temperatures and are not thermally stable at high temperatures. Therefore, conventional methods for constructing refractory layer systems are not adequate to develop GaAs semiconductors which are thermally stable at temperatures above 450.degree. C. during continuous periods of up to about 24 hours of thermal stress.